A wireless link, typically enabled by a radio (although possibly enabled by a light source or even a sound source), is used to remotely control an unmanned ground vehicle (UGV) or other unmanned vehicle or device that moves in some respect (e.g. it swivels), all of which are called here a remote controlled device (RCD), from what is here called an operator control unit (OCU). To control the RCD, commands are sent by an operator from the OCU to the RCD using the wireless link, i.e. using e.g. radio signals, and often using radio signals modulated by a digital encoding of the information (commands) to be sent to the RCD.
In the other direction, from the RCD to the OCU, the RCD provides a video signal to the OCU, and the operator of the RCD examines the video signal in deciding what commands to send to the RCD, i.e. in order to remotely control the RCD. The video signal is a stream of images, i.e. a video stream, and, like the commands, the video is typically digitally encoded and in case of a radio-enabled wireless link, it is the digitally encoded video that is used to modulate the radio signal.
The video data stream is a stream of video frames, each at some resolution, which may differ from frame to frame. The operator controls the motion of the RCD, including how fast the RCD moves, e.g. its rate of travel over the ground or its rate of swivel, by sending commands to the RCD over the wireless link, using the available bandwidth of the wireless link.
In radio communications using a modulated carrier, bandwidth, as that term is used here, is the range of frequencies occupied by the modulated carrier, i.e. the range of frequencies for which the Fourier transform of the modulated radio signal is non-zero (or above some minimum level). In digital wireless communication, as mentioned, the information is digitally encoded according to some coding scheme, and it is that information that is used to modulate the carrier, according to one or another modulation scheme (and in some cases there can be a quite blurry line between modulation and coding, even to the extent that the two can be said to be combined, as in trellis coded modulation).
Typically, in remotely controlling an RCD using a digital radio (i.e. using a wireless link enabled by a radio transmitting a radio signal modulated be digitally encoded information), the modulation and coding scheme are fixed, and so the maximum available bandwidth is typically fixed (unvarying). Although the available bandwidth is typically fixed, the quality of the radio link varies, depending on the radio-frequency noise present in the environment, the power used to transmit a signal, and the distance between the RCD and OCU, among other things. If the quality of the radio link degrades too much to accommodate the rate of data being communicated between the radio units, the radio link fails, i.e. communication between the RCD and the OCU is at least temporarily lost. The failure is abrupt in case of using a constant data rate, independent of the quality of the data rate; i.e. in such a case, the operator is surprised. During the time required to reestablish the link, the RCD is out of control (and is usually configured to stop and wait for the radio link to reestablish). Sometimes the link can be reestablished, but if e.g. the RCD is too far away to accommodate the video data and commands, control is lost. The link could also be lost if the RF environment has changed too much, e.g. in case of a hostile attempt to jam communication between the RCD and OCU.
It is therefore desirable to alter the rate at which the RCD sends data to the OCU, to take into account the quality of the radio link.
Some prior art radio communication systems do alter the data rate provided by a radio link, in order to adapt to situations where the radio link is deteriorating. However, such radio links use a more complex communication protocols than are typically used in case of RCDs, namely layered communication protocols that ensure data integrity. These layered communications protocols typically include, at both ends of a communication link, what is sometimes called a network layer (and sometimes called an Internet layer). These so-called peer layers (at the two ends of a link) exchange (in peer-to-peer communication) information useful in determining how to alter the radio link to adapt to changes in the error rate of communication. TCP/IP (Transmission Control Protocol/Internet Protocol) is such a protocol.
In case of RCDs providing video data there is no need to ensure data integrity (since a portion of a video image may be damaged and the video image still serves a useful purpose). Instead of TCP/IP, therefore, RCDs use UDP (User Datagram Protocol), which is a simple protocol that in effect says, “send the data into the world; I don't care about who receives it, I don't care if it ever gets there, just send it.” In case of using UDP, there is no network layer providing information indicating how much data has actually been received during a communication.
The prior art also teaches using feedback to an RCD provided by the OCU controlling the RCD, for the RCD to use in determining how to alter the data rate transmitted by the RCD. (It is only the rate of data sent from the RCD to the OCU that is at issue, since the data rate required to send commands to the RCD from the OCU is small.) However, providing such feedback consumes bandwidth, i.e. the wireless link has only so much capacity for communicating information between the OCU and the RCD, and providing feedback from the OCU on the quality of the wireless link eats into that capacity.
In all of this prior art, use of the bandwidth is altered based on some feedback from the OCU.
What is needed is a way to control use of the radio link without relying on information provided by a network layer, since there is typically no such layer, and without relying on any other feedback from the OCU. Ideally, the use of the radio link is an intelligent use that takes into account whether the radio link is better used for more frames at lower resolution, or fewer frames at higher resolution.